Previous evaluation of lymphocytes taken from patients with Wiskott-Aldrich syndrome (WAS) and other X-linked immunodeficiencies has revealed deficiencies of a lymphocyte sialoglycoprotein with a relative molecular mass of 115 kD (designated gpL-115) found in normal lymphocytes. The development of monoclonal antibodies to gpL-115 has permitted the detection of molecular heterogeneity in gpL-115 from the lymphocytes of immunodeficient patients. When lymphocytes from normal individuals were analyzed by immunoblotting, gpL-115 with only a single molecular species (115 kD) was detected. Lymphocytes from 17 immunodeficient patients were analyzed after overnight incubation. Two patients had no gpL-115 with an Mr of 115 kD, but gpL-115 with an Mr of either 95 or 135 kD was detected. Nine patients had gpL-115 with Mr equally of 95 and 115 Kd. Other patients exhibited gpL-115 with combinations of 95, 115, and 135 kD. The heterogeneity of the degraded gpL-115 suggests that WAS and other X-linked immunodeficiencies are due to a series of abnormalities, all of which involve gpL-115, and may explain the clinical heterogeneity of the diseases.